CODEWITHSUNDEEP
javalambdafunctional-programmingjava-8java-stream
peter
peter

Reputation: 8473

Java8 Stream as a whole maps to a Function

I am wondering if there's a better way to rewrite the groupA method with lambda as part of the chaining operations ?

public class Id {
    private final int value;
    public Id(int value) {
       this.value = value;
    }

    public int value() {
       return value;
    }
}

public class Ids implements Iterable<Id> { 
   private final List<Id> ids;

   private Ids(List<Id> ids) {
      this.ids = ids;
   }

   public static Ids of(List<Id> ids) {
      return new Ids(ids);
   }

   public Ids groupA() {
      return Ids.of(ids.stream()
                       .filter(id -> id.value() > 5)
                       .collect(Collectors.toList()));
   }

   @Override
   public Iterator<Id> iterator() {
      return ids.iterator();
   }
}

Basically I want to do something like

ids.stream()
   .filter(id -> id % 10 > 5)
   .collect(Collectiors.toList())
   .andThen(Ids::of);

And wonder if that's possible

Upvotes: 2

Views: 111

Answers (2)

Tagir Valeev
Tagir Valeev

Reputation: 100209

In my StreamEx library there's a shortcut method toListAndThen which makes this looking more fluent:

StreamEx.of(ids)
  .filter(id -> id % 10 > 5)
  .toListAndThen(Ids::of);

Upvotes: 2

Louis Wasserman
Louis Wasserman

Reputation: 198103

Sure. You can either just do the straightforward

Ids.of(ids.stream()
   .filter(id -> id % 10 > 5)
   .collect(Collectors.toList()))

or you could add it to the collector:

ids.stream()
   .filter(id -> id % 10 > 5)
   .collect(Collectors.collectingAndThen(Collectors.toList(), Ids::of))

Upvotes: 10

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